Heat exchanger

ABSTRACT

The invention relates to heat exchangers for use in motor vehicles or for industrial use, for example, to heat exchangers for use as evaporators, condensers, oil coolers, intercoolers, heater cores, etc. The invention provides a heat exchanger comprising pairs of plates with each plate of the pair having formed on one side thereof a peripheral ridge, central ridge and channel dividing U-shaped ridges which are formed by forging or cutting. Each pair of plates are fitted together and joined, with channel recesses thereof opposed to each other to form a flat tube and a plurality of U-shaped divided fluid passageways in a U-shaped fluid channel inside the tube. Each pair of adjacent flat tubes are joined by spectacle-shaped header members interposed between the upper ends of the tubes and each comprising a front and a rear fluid passing tube portion and a connecting portion therebetween to provide a front and a rear header in communication with the upper ends of the flat tubes.  
     The flat tubes have a reduced front-to-rear width, diminished wall thickness (thinner layers) and increased heat transfer efficiency to provide a heat exchanger which achieves a higher heat transfer efficiency and greatly improved heat exchange performance.

CROSS REFERENCE TO RELATED APPLICATIONS

[0001] This application is an application filed under 35 U.S.C. §111(a)claiming the benefit pursuant to 35 U.S.C. §119(e)(1) of the filing dataof Provisional Application No. 60/302,371 filed Jul. 3, 2001 pursuant to35 U.S.C. §111(b).

TECHNICAL FIELD

[0002] The present invention relates to heat exchangers for use in motorvehicles or for industrial use, for example, to heat exchangers for useas evaporators, condensers, oil coolers, intercoolers, heater cores,etc.

[0003] Generally aluminum heat exchangers are conventionally in wide useas heat exchangers, especially as evaporators for motor vehicle airconditioners, from the viewpoint of lightweightness and workabiliy.

[0004] At present, evaporators for motor vehicle air conditioners arechiefly those of the laminate type (layered type). In fabricatingevaporators of this type, heat exchange fins for air and a tube portionfor evaporating the refrigerant are joined together by brazing, so thatsuch evaporators are superior to heat exchangers of the fin tubeenlarged type which were previously in use, for example, with respect toperformance and productivity. These evaporators are exceedingly superiorto the fin tube enlarged type especially in performance characteristicssince louver fins of high heat transfer efficiency are usable as airfins for this type of evaporators to ensure an increased quantity ofheat exchange and low resistance to the flow of air.

[0005] Accordingly, more lightweight and compact heat exchangers aremade available to meet the market demand for smaller sizes and reducedweight. Especially recently, many evaporators are provided with a filteron the front side in view of problems involved in the vehiclecompartment, and it has been strongly required that heat exchangers bereduced in thickness to provide space for the installation of thefilter.

[0006] For example as shown in FIG. 25, conventional heat exchangers foruse as evaporators comprise generally rectangular aluminum plates 62each having formed in one surface thereof front and rear refrigerantchannel forming recessed porions 66 divided by a vertically elongatedpartition ridge 64, and header forming recessed portions (not shown)respectively continuous with the upper and lower ends of these recessedportions 66 and having a larger depth than these portions 66. Each pairof adjacent plates 62 are fitted together in superposed layers withtheir recessed surfaces opposed to each other to join the opposedpartition ridges 64, 64 of the plates 62, 62 to each other and opposedperipheral edges 63, 63 thereof to each other and to thereby form a flattube portion 61 having front and rear flat refrigerant channels 68 andupper and lower header portions continuous with the respective channels68. A multiplicity of such flat tube portions 61 are arranged inparallel with a fin interposed therebetween for air to provide the heatexchanger. Each of the plates 62 is prepared from an aluminum sheet bypress forming.

[0007] The conventional heat exchanger for use as an evaporatorencounters the following problems in fulfilling the commercial demandfor a reduced thickness.

[0008] (1) The plates 62 for forming the flat tube portion 61 are madefrom an aluminum sheet by drawing with use of a press, so that thepartition ridge 64 and the peripheral edge 63 have an increased width.Accordingly, the joints between the two plates 62, 62, i.e., the jointof the opposed partition ridges of the plates 62, 62 and the joint ofthe opposed peripheral edges 63, 63 which are useless portions notpassing the refrigerant have a relatively great area, which consequentlyreduces the cross sectional area of the refrigerant channel when theevaporator has a given volume, offering increased resistance to the flowof the refrigerant and resulting in impaired performance.

[0009] To meet this problem, it appears useful to give an increasedheight to the refrigerant channel and thereby assure the channel of asufficient cross sectional area, whereas the volume to be occupied bythe air-side fin in the given volume will then decrease. Thus, the finhas a smaller area for heat transfer and is impaired in performance,while a diminished air passage produces increased resistance to the flowof air, failing to afford a proper rate of air flow.

[0010] (2) On the other hand, the joint between the peripheral edges 63,63 of the two plates 62, 62 is out of direct contact with the fin forthe air side to exhibit a low heat transfer efficiency, so that areduction in the thickness of the heat exchanger including such uselessportions increases the relative ratio in area of the useless portionsnot participating in the passage of the refrigerant.

[0011] (3) The header forming recessed portions of the plate 62 aregiven a greater depth than the front and rear refrigerant channelforming recessed portions 66, 66 on opposite sides of the partitionridge 64 by being worked by drawing, and are therefore made smaller inwall thickness than the recessed portions 66. Although the flat tubeportion 61 having a great proportion is given an allowance for pressureresistance, the header portions are weakest against pressure. With theconventional heat exchanger, the flat tube portion 61 and the headerportions are made from an integral plate material, and that by presswork, so that there are limitations in further reducing the headerportions in wall thickness and weight.

[0012] An object of the present invention is to overcome the foregoingtechnical problems of the prior art and to provide a heat exchangerwhich is fabricated from plates having ridges and recessed portionsformed in one surface thereof as by forging or cutting work instead ofusing plates formed by press work and in which headers are formed from amember separate from the plate to make a flat tube having a reducedfront-to-rear width, a diminished wall thickness (layer of diminishedthickness) and an increased heat transfer area, the heat exchanger thusbeing adapted to achieve a higher heat transfer efficiency and greatlyimproved heat exchange performance.

DISCLOSURE OF THE INVENTION

[0013] First, the present invention provides a heat exchanger which ischaracterized in that the heat exchanger comprises pairs of plates witheach plate of the pairs having a peripheral ridge provided on one sideof the plate along a periphery thereof and a central ridge provided onsaid one side of the plate at a center of the width thereof andextending downward from an upper end of the plate to a position where areturn channel can be formed, the ridges being formed by forging orcutting, each plate of said pairs having a U-shaped channel recessformed inwardly of the peripheral ridge and comprising a front and arear channel recess portion formed on opposite sides of the centralridge and a return channel recess portion positioned under the centralridge, the channel recess having one of two fluid inlet-outlet throughholes formed at one end thereof and the other through hole formed at theother end thereof, each plate of said pairs having a flat surface on theother side thereof, each of said pairs of plates being fitted togetherwith their U-shaped channel recesses opposed to each other to join theopposed peripheral ridges to each other end-to-end and the opposedcentral ridges to each other end-to-end and to thereby form a flat tubehaving a U-shaped fluid channel inside thereof so that a plurality offlat tubes are arranged in parallel with a header member interposedbetween upper ends of each pair of adjacent flat tubes to provide afront and a rear header in communication with the upper ends of the saidpair of adjacent flat tubes, the header member comprising a pair offront and rear fluid passing tube portions in communications with therespective inlet-outlet through holes of the plates of said pair ofadjacent flat tubes and a connecting portion between the tube portions.

[0014] Second, the present invention provides a heat exchanger which ischaracterized in that the heat exchanger comprises pairs of plates witheach plate of the pairs having an edge ridge U-shaped in its entiretyand provided on one side of the plate along opposite side edges and alower edge thereof and a central ridge provided on said one side of theplate at a center of the width thereof and having a bifurcated upperend, the central ridge extending from the upper end downward to aposition where a return channel can be formed, the ridges being formedby forging or cutting, each plate of said pairs having a U-shapedchannel recess formed inwardly of the U-shaped edge ridge and comprisinga front and a rear channel recess portion formed on opposite sides ofthe central ridge and a return channel recess portion positioned underthe central ridge, each plate of said pairs having a flat surface on theother side thereof, each of said pairs of plates being fitted togetherwith their U-shaped channel recesses opposed to each other to join theopposed U-shaped edge ridges to each other end-to-end and the opposedcentral ridges including the bifurcated upper ends to each otherend-to-end and to thereby form a flat tube having bifurcated open upperends and a U-shaped fluid channel inside thereof, a pair of front andrear header members being each in the form of a pipe having arectangular cross section, each of the header members having slitsformed in a lower wall thereof and arranged at a predetermined spacing,a plurality of flat tubes being arranged in parallel by inserting thebifurcated open upper ends thereof into the respective slits in thefront and rear header members to join the flat tubes to the headermembers and to provide a front and a rear header in communication withthe bifurcated open upper ends of the flat tubes.

[0015] With the heat exchanger having the first or second featuredescribed, a plurality of channel dividing U-shaped ridges are formed inthe U-shaped channel recess of each plate by forging or cutting, and apluralty of U-shaped divided fluid passageways are formed in theU-shaped fluid channel in the interior of each flat tube. The inventionprovides several modes of channel dividing ridges.

[0016] As a first mode, a plurality of channel dividing U-shaped ridgesare formed in the U-shaped channel recess of each plate by forging orcutting, and each said pair of plates are fitted together with therecesses thereof opposed to each other and with each of opposed pairs ofchannel dividing U-shaped ridges joined to each other end-to-end to forma plurality of U-shaped divided fluid passageways in the U-shaped fluidchannel inside the flat tube.

[0017] A second mode of channel dividing ridges is as follows. Eachplate of said pairs has formed in the channel recess thereof front andrear channel dividing ridges having a height twice the depth of thechannel recess and each comprising a straight portion positioned in thefront or rear straight channel recess portion of the channel recess anda quarter circular-arc portion extending from a lower end of thestraight portion and positioned in the return portion of the channelrecess, the channel dividing ridges being formed by forging or cuttingand positioned alternately when each of said pairs of plates are fittedtogether with their channel recesses opposed to each other, each of saidpairs of plates being fitted together with their channel recessesopposed to each other to join top ends of the front and rear channeldividing ridges to a bottom wall flat surface of the plate providing thechannel recess and opposed thereto and to thereby form U-shaped dividedfluid passageways in the U-shaped fluid channel inside the flat tube.

[0018] A third mode of channel dividing ridges is as follows. Each plateof said pairs has formed in the channel recess thereof channel dividingridges having a height twice the depth of the channel recess and formedby forging or cutting so as to be positioned alternately, when each ofsaid pairs fitted together with the recesses thereof opposed to eachother, each of said pairs of plates being fitted together to join topends of the channel dividing ridges on each plate of the pair to a flatsurface of bottom wall of the channel recess of the other plate opposedto said each plate and to thereby form U-shaped divided fluidpassageways in the U-shaped fluid channel inside the flat tube.

[0019] A fourth mode of channel dividing ridges is as follows. Eachplate of said pairs has formed in a rear half of the channel recessthereof channel dividing ridges having a height twice the depth of thechannel recess and formed by forging or cutting, the channel recess ofeach plate having a front half in the form of a flat surface provided bya bottom wall thereof and having no channel dividing ridges, each ofsaid pairs of plates being fitted together with the recesses thereofopposed to each other to join top ends of the channel dividing ridgesthereof to the bottom wall flat surface of the channel recess of theplate opposed to the dividing ridges and to thereby form U-shapeddivided fluid passageways in the U-shaped fluid channel inside the flattube.

[0020] With the heat exchanger having the first feature of theinvention, one of each pair of plates may be replaced by a flat plate.

[0021] More specifically, the heat exchanger in this case comprisesridged plates each having a peripheral ridge provided on one side of theplate along a periphery thereof and a central ridge provided on said oneside of the plate at a center of the width thereof and extendingdownward from an upper end of the plate to a position where a returnchannel can be formed, the ridges being formed by forging or cutting,each of the ridged plates having a U-shaped channel recess formedinwardly of the peripheral ridge and comprising a front and a rearchannel recess portion formed on opposite sides of the central ridge anda return channel recess portion positioned under the central ridge, thechannel recess having one of two fluid inlet-outlet through holes formedat one end thereof and the other through hole formed at the other endthereof, each of the ridged plates having a flat surface on the otherside thereof and being fitted to each of flat plates face-to-face, eachof said flat plates having the same contour and the same size as theridged plate and two fluid inlet-outlet through holes corresponding tosaid through holes, the peripheral ridge of the ridged plate having atop end thereof joined to a peripheral edge of the flat plate, thecentral ridge of the ridged plate having a top end thereof joined to aflat surface of a corresponding central portion of the flat plate,whereby a flat tube having a U-shaped fluid channel inside thereof isformed so that a plurality of flat tubes are arranged in parallel with aheader member interposed between upper ends of each pair of adjacentflat tubes to provide a front and a rear header in communication withthe upper ends of the said pair of adjacent flat tubes, the headermember comprising a pair of front and rear fluid passing tube portionsin communications with the respective inlet-outlet through holes of theplates of said pair of adjacent flat tubes and a connecting portionbetween the tube portions.

[0022] With the heat exchanger having the second feature of theinvention, one of each pair of plates may be replaced by a flat plate.

[0023] Stated more specifically, the heat exchanger in this casecomprises ridged plates each having an edge ridge U-shaped in itsentirety and provided on one side of the plate along opposite side edgesand a lower edge thereof and a central ridge provided on said one sideof the plate at a center of the width thereof and having a bifurcatedupper end, the central ridge extending from the upper end downward to aposition where a return channel can be formed, the ridges being formedby forging or cutting, each of the ridged plates having a U-shapedchannel recess formed inwardly of the U-shaped edge ridge and comprisinga front and a rear channel recess portion formed on opposite sides ofthe central ridge and a return channel recess portion positioned underthe central ridge, each of the ridged plates having a flat surface onthe other side thereof and being fitted to each of flat platesface-to-face, each of said flat plates having the same contour and thesame size as the ridged plate, the peripheral ridge of the ridged platehaving a top end thereof joined to a peripheral edge of the flat plate,the central ridge of the ridged plate including the bifurcated upperends having a top end thereof joined to a flat surface of acorresponding central portion of the flat plate, whereby a flat tubehaving bifurcated open upper ends and a U-shaped fluid channel insidethereof is formed, a pair of front and rear header members being each inthe form of a pipe having a rectangular cross section, each of theheader members having slits formed in a lower wall thereof and arrangedat a predetermined spacing, a plurality of flat tubes being arranged inparallel by inserting the bifurcated open upper ends thereof into therespective slits in the front and rear header members to join the flattubes to the header members and to provide a front and a rear header incommunication with the bifurcated open upper ends of the flat tubes.

[0024] In a heat exchanger having such flat plates, a plurality ofchannel dividing U-shaped ridges are formed in the U-shaped channelrecess of each ridged plate by forging or cutting, and each ridged plateand each flat plate are fitted together face-to-face with the channeldividing U-shaped ridges of the ridged plate joined to the flat surfaceof the corresponding central portion of the flat plate to form aplurality of U-shaped divided fluid passageways in the U-shaped fluidchannel inside the flat tube.

[0025] Third, the present invention provides a heat exchanger which ischaracterized in that the heat exchanger comprises pairs of plates witheach plate of the pairs having a peripheral ridge provided on one sideof the plate along a periphery thereof and a central ridge provided onsaid one side of the plate at a center of the width thereof andextending vertically, the ridges being formed by forging or cutting,each plate of said pairs having a front and a rear channel recessportion formed inwardly of the peripheral ridge on opposite sides of thecentral ridge, each of the front and rear channel recess portions havinga through hole formed in each of upper and lower ends thereof, eachplate of said pairs having a flat surface on the other side thereof,each of said pairs of plates being fitted together with their channelrecess portions opposed to each other to join the opposed peripheralridges to each other end-to-end and the opposed central ridges to eachother end-to-end and to thereby form a flat tube having a front and arear fluid channel inside thereof so that a plurality of flat tubes arearranged in parallel with an upper and a lower header member interposedrespectively between upper ends of each pair of adjacent flat tubes andbetween lower ends thereof to provide an upper and a lower header incommunication with the upper ends and the lower ends of said pair ofadjacent flat tubes, each of the header members comprising a pair offront and rear fluid passing tube portions in communications with thecorresponding through holes of the plates of said pair of adjacent flattubes and a connecting portion between the tube portions.

[0026] Fourth, the present invention provides a heat exchanger which ischaracterized in that the heat exchanger comprises pairs of plates witheach plate of the pairs having a side edge ridge provided on one side ofthe plate along each of opposite side edges thereof and a central ridgeprovided on said one side of the plate at a center of the width thereofand having a bifurcated upper and a bifurcated lower end, the ridgesbeing formed by forging or cutting, each plate of said pairs having afront and a rear channel recess portion formed inwardly of the side edgeridges on opposite sides of the central ridge, each plate of said pairshaving a flat surface on the other side thereof, each of said pairs ofplates being fitted together with their channel recess portions opposedto each other to join the opposed side edge ridges to each otherend-to-end and the opposed central ridges including the bifurcated upperand lower ends to each other end-to-end and to thereby form a flat tubehaving bifurcated open upper and lower ends and a front and a rear fluidchannel inside thereof, an upper pair of front and rear header membersand a lower pair of front and rear header members being each in the formof a pipe having a rectangular cross section, each of the header membershaving slits formed in an upper wall or a lower wall thereof andarranged at a predetermined spacing, a plurality of flat tubes beingarranged in parallel by inserting the bifurcated upper or lower endsthereof into the respective slits in the header members to join the flattubes to the header members and to provide an upper pair of front andrear headers and a lower pair of front and rear headers in communicationwith the bifurcated upper and lower ends of the flat tubes respectively.

[0027] With the heat exchanger having the third or fourth featuredescribed, a plurality of channel dividing ridges are formed in thefront and rear channel recesses of each plate by forging or cutting, anda pluralty of divided fluid passageways are formed in the front and rearfluid channels in the interior of each flat tube. The invention providesseveral modes of channel dividing ridges.

[0028] As a first mode, a plurality of channel dividing ridges areformed in the front and rear channel recess portions of each plate byforging or cutting, and each of said pairs of plates are fitted togetherwith their recess portions opposed to each other to join each of opposedpairs of the channel dividing ridges to each other end-to-end and formdivided fluid passageways in the front and rear fluid channels insidethereof.

[0029] A second mode of channel dividing ridges is as follows. Eachplate has formed in the respective front and rear channel recessportions thereof front and rear channel dividing ridges having a heighttwice the depth of the recess portion, the front and rear channeldividing ridges being formed by forging or cutting and positionedalternately when each of said pairs of plates are fitted together withtheir recess portions opposed to each other, each of said pairs ofplates being fitted together face-to-face to join top ends of the frontand rear channel dividing ridges to a bottom wall flat surface of recessportion of the plate opposed thereto and to thereby form divided fluidpassageways in the front and rear fluid channels inside the flat tube.

[0030] A third mode of channel dividing ridges is as follows. Each plateof the pairs has formed in each of the front and rear channel recessportions thereof a channel dividing ridge having a height twice thedepth of the recess portion, the channel dividing ridge being so formedby forging or cutting that the front and rear channel dividing ridges ofeach pair of plates as fitted together face-to-face are positionedalternately, each pair of plates being fitted together with their recessportions opposed to each other to join top ends of the front and rearchannel dividing ridges of each plate of the pair to a bottom wall flatsurface of the recess portion of the other plate of the pair opposedthereto and to thereby form divided fluid passageways in the front andrear fluid channels inside the flat tube.

[0031] A fourth mode of channel dividing ridges is as follows. Eachplate has formed in one of the front and rear channel recess portionsthereof a plurality of channel dividing ridges having a height twice thedepth of the recess portion, the channel dividing ridges being formed byforging or cutting, the other channel recess portion having a bottomwall flat surface having no channel dividing ridges, each of said pairsof plates being fitted together with their recess portions opposed toeach other to join top ends of the channel dividing ridges to the bottomwall flat surface of the recess portion of the plate opposed thereto andto thereby form divided fluid passageways in the front and rear fluidchannels inside the flat tube.

[0032] With the heat exchanger having the third feature of theinvention, one of each pair of plates may be replaced by a flat plate.

[0033] Stated more specifically, the heat exchanger in this casecomprises ridged plates each having a peripheral ridge provided on oneside of the plate along a periphery thereof and a central ridge providedon said one side of the plate at a center of the width thereof andextending vertically, the ridges being formed by forging or cutting,each the ridged plates having a front and a rear channel recess portionformed inwardly of the peripheral ridge on opposite sides of the centralridge, each of the front and rear channel recess portions having athrough hole formed in each of upper and lower ends thereof, each of theridged plates having a flat surface on the other side thereof and beingfitted to each of flat plates face-to-face, each of said flat plateshaving the same contour and the same size as the ridged plate and fluidinlet-outlet through holes corresponding to said through holes, theperipheral ridge of the ridged plate having a top end thereof joined toa peripheral edge of the flat plate, the central ridge of the ridgedplate having a top end thereof joined to a flat surface of acorresponding central portion of the flat plate, whereby a flat tubehaving a front and a rear fluid channel inside thereof is formed so thata plurality of flat tubes are arranged in parallel with an upper and alower header member interposed respectively between upper ends of eachpair of adjacent flat tubes and between lower ends thereof to provide anupper and a lower header in communication with the upper ends and thelower ends of said pair of adjacent flat tubes, each of the headermembers comprising a pair of front and rear fluid passing tube portionsin communications with the corresponding through holes of the plates ofsaid pair of adjacent flat tubes and a connecting portion between thetube portions.

[0034] In the above heat exchanger, the connecting portion of one of theupper and lower header members interposed between the upper ends andlower ends of each pair of adjacent flat tubes may have a passageinterconnecting the fluid passing tube portions of the header member.

[0035] With the heat exchanger having the fourth feature of theinvention, one of each pair of plates may be replaced by a flat plate.

[0036] Stated more specifically, the heat exchanger then comprisesridged paltes each having a side edge ridge provided on one side of theplate along each of opposite side edges thereof and a central ridgeprovided on said one side of the plate at a center of the width thereofand having a bifurcated upper and a bifurcated lower end, the ridgesbeing formed by forging or cutting, each of the ridged plates having afront and a rear channel recess portion formed inwardly of the side edgeridges on opposite sides of the central ridge, each of the ridged plateshaving a flat surface on the other side thereof and being fitted to eachof flat plates face-to-face, each of said flat plates having the samecontour and the same size as the ridged plate, the side edge ridges ofthe ridged plate having top ends thereof joined to side edges of theflat plate, the central ridge of the ridged plate including thebifurcated upper and lower ends having a top end thereof joined to aflat surface of a corresponding central portion of the flat plate,whereby a flat tube having bifurcated open upper and lower ends and afront and a rear fluid channel inside thereof is formed, an upper pairof front and rear header members and a lower pair of front and rearheader members being each in the form of a pipe having a rectangularcross section, each of the header members having slits formed in anupper wall or a lower wall thereof and arranged at a predeterminedspacing, a plurality of flat tubes being arranged in parallel byinserting the bifurcated upper or lower ends thereof into the respectiveslits in the header members to join the flat tubes to the header membersand to provide an upper pair of front and rear headers and a lower pairof front and rear headers in communication with the bifurcated upper andlower ends of the flat tubes respectively.

[0037] In a heat exchanger wherein flat plates are used, each of theridged plates has channel dividing ridges formed in the respective frontand rear channel recess portions thereof by forging or cutting, and eachridged plate is fitted to each flat plate face-to-face to join top endsof the channel dividing ridges to a flat surface of a correspondingportion of the flat plate and to thereby form divided fluid passagewaysin the front and rear fluid channels inside the flat tube.

[0038] In a heat exchanger which has the first or third feature, theheader member interposed between the ends of each pair of adjacent flattubes has its fluid passing tube portions joined at their opposite endfaces to the flat surfaces on the other sides of the opposed plates ofthe pair of flat tubes. Preferably, tacks for temporarily holding theheader member are provided on respective edges defining the inlet-outletthrough holes in the end of each plate.

[0039] In a heat exchanger according, a plurality of cutouts are formedin the channel dividing ridges on each plate to cause the adjacentdivided fluid passageways inside the flat tube to communicate with eachother through the cutouts.

[0040] In any of the heat exchangers of the invention described, a finis provided between each pair of adjacent flat tubes included in theflat tubes arranged in parallel, and the fin has opposite sides edgesthereof joined to the flat surfaces on the other sides of the plates ofthe pair of flat tubes.

[0041] For use in any of the heat exchangers of the invention described,the plates are those having recesses and ridges formed on one sidethereof by forging or cutting, in place of conventional plates which areformed by press work, and the header members are members separate fromthe plate for providing headers. These features provide flat tubeshaving a reduced front-to-rear width, a diminished wall thickness (layerof diminished thickness) and an increased heat transfer area to resultin the advantages of a higher heat transfer efficiency and greatlyimproved heat exchange performance.

BRIEF DESCRIPTION OF THE DRAWINGS

[0042]FIG. 1 is a perspective view of a heat exchanger according to afirst embodiment of the invention.

[0043]FIG. 2 is an enlarged front view of a plate of the heat exchangerof FIG. 1.

[0044]FIG. 3 is an enlarged fragmentary perspective view of the plate.

[0045]FIG. 4 is an enlarged exploded fragmentary perspective view of theheat exchanger of FIG. 1.

[0046]FIG. 5 is an enlarged cross sectional view of a plate tube of theheat exchanger.

[0047]FIG. 6 is an enlarged fragmentary perspective view partly brokenaway and showing the heat exchanger.

[0048]FIG. 7 is an enlarged fragmentary cross sectional view showing amodification of dividing ridges of plate of the heat exchanger of FIG.1.

[0049]FIG. 8 is an enlarged front view showing a modified plate of theheat exchanger.

[0050]FIG. 9 is an enlarged fragmentary perspective view showing anothermodified plate of the heat exchanger.

[0051]FIG. 10 is an enlarged cross sectional view of a flat tube for theheat exchanger wherein the plate of FIG. 9 is used.

[0052]FIG. 11 is an enlarged exploded fragmentary perspective view of aheat exchanger according to a second embodiment of the invention.

[0053]FIG. 12 is an enlarged fragmentary front view of the plate of theheat exchanger of FIG. 11, with headers also shown.

[0054]FIG. 13 is a perspective view of a heat exchanger according to athird embodiment of the invention.

[0055]FIG. 14 is an enlarged front view of the plate of the heatexchanger plate shown FIG. 13.

[0056]FIG. 15 is an enlarged fragmentary perspective view of the heatexchanger plate.

[0057]FIG. 16 is an enlarged exploded perspective view of an upper endportion of the heat exchanger.

[0058]FIG. 17 is an enlarged exploded perspective view of a lower endportion of the heat exchanger.

[0059]FIG. 18 is an enlarged front view of a plate for use in the heatexchanger of FIG. 1 to show a second modification of diving ridges.

[0060]FIG. 19 is an enlarged cross sectional view of a flat tube for theheat exchanger wherein the plate of FIG. 18 is used.

[0061]FIG. 20 is an enlarged front view of a plate for use in the heatexchanger of FIG. 1 to show a third modification of diving ridges, theplate being one of a pair of plates in combination.

[0062]FIG. 21 is an enlarged front view of the other plate of the pair.

[0063]FIG. 22 is an enlarged front view of a plate for use in the heatexchanger of FIG. 1 to show a fourth modification of diving ridges.

[0064]FIG. 23 is an enlarged cross sectional view of a flat tube for theheat exchanger wherein the plate of FIG. 22 is used.

[0065]FIG. 24 is an enlarged cross sectional view of a flat tube of heatexchanger of the invention, wherein one of a pair of plates incombination is replaced by a flat plate as a modification.

[0066]FIG. 25 is an enlarged cross sectional view of a flat tube of anexample of conventional heat exchanger.

BEST MODE OF CARRYING OUT THE INVENTION

[0067] Embodiments of the present invention will be described below withreference to the drawings.

[0068] The terms “front,” “rear,” “left,” “right,” “upper” and “lower”as used herein are based on FIG. 2; “front” refers to the left-hand sideof FIG. 2, “rear” to the right-hand side thereof, “left” to the frontside of the plane of the drawing, “right” to the rear side of the planethereof, “upper” to the upper side of the drawing, and “lower” to thelower side thereof.

[0069] The drawings show heat exchangers of the invention for use asevaporators for motor vehicle air conditioners.

[0070] FIGS. 1 to 6 show a first embodiment of the present invention. Aheat exchanger 1 for use as an evaporator is made from aluminum(including aluminum alloys).

[0071] A generally rectangular plate 2 made of an aluminum plate has aperipheral ridge 3 provided on one side of the plate 2 along a peripherythereof and a central ridge 4 provided on the same side of the plate 2at the center of the width thereof and extending downward from the upperend of the plate to a position where a refrigerant return channel can beformed. Formed in the plate 2 internally of the peripheral ridge 3 is aU-shaped refrigerant channel recess 6 comprising front and rear straightrefrigerant channel recess portions 6 a, 6 b positioned on oppositesides of the central ridge 4 and a refrigerant return channel recessportion 6 c positioned under the central ridge.

[0072] According to this first embodiment, the plate 2 is provided inthe widthwise midportion of its upper end with a notch 14 which isU-shaped when seen from the front. The central ridge 4 is joined at itsupper end to the peripheral ridge 3 at the lower end of this notch 14.

[0073] The channel recess 6 has one of refrigerant inlet-outlet throughholes 10, 10 formed at one end thereof and the other through hole 10formed at the other end thereof. The plate 2 has a plurality of channeldiving U-shaped ridges 5 formed inside the channel recess 6 andextending over the approximate entire length thereof.

[0074] The presence of the notch 14 in the widthwise midportion of upperend of the plate 2 positions the though holes 10, 10 as spaced apartfrom each other by the width of the notch 14. This serves to preventunnecessary heat exchange between an incoming portion of refrigeranthaving a low temperature and an outgoing portion of refrigerant having ahigh temperature, and to prevent the refrigerant introduced into aninlet header to be described later from flowing into an outlet headerthrough a short path.

[0075] The corners of return channel recess portion 6 c of the channelrecess 6 have short circular-arc ridges 9 for achieving an improved heatexchange efficiency at the corner portions.

[0076] Each plate 2 is formed, for example, by forging or cutting.Plates 2 are provided in pairs, and each pair of plates 2 are fittedtogether with their U-shaped channel recesses 6, 6 opposed to each otherto join the opposed peripheral ridges 3, 3 of the plates 2, 2 to eachother end-to-end, the opposed central ridges 4, 4 thereof to each otherend-to-end and each of the opposed pairs of channel dividing rides 5, 5to each other end-to-end and to thereby form a flat tube 12 having aU-shaped refrigerant channel 8 inside thereof, with a plurality ofU-shaped divided refrigerant passageways 7 formed in the refrigerantchannel 8 inside the flat tube 12.

[0077] A clad material is used for each plate 2 which has a brazingsheet affixed to one surface thereof, preferably each of the inner andouter surfaces thereof. Such components can then be joined togethereasily.

[0078] The evaporator 1 of the present invention has headers 23, 23which interconnect flat tubes 12, 12 providing a refrigerant circuit andwhich are formed in the following manner.

[0079] A plurality of flat tubes 12 are arranged in parallel, with aspectacle-shaped header member 20 interposed between the upper ends ofeach pair of adjacent flat tubes 12, 12 to provide front and rearheaders 23, 23 in communication with the upper ends of the pair ofadjacent flat tubes 12. The header member 20 comprises a pair of frontand rear refrigerant passing tube portions 21, 21 in communications withthe respective inlet-outlet through holes 10, 10 of the plates 2 and aconnecting portion 22 between the tube portions. Opposite end faces offront and rear tube portions 21, 21 of the header member 20 are joinedto flat surfaces provided by the other sides of respective opposedplates 2, 2 of the pair of flat tubes 12.

[0080] Below the headers 23, 23, a corrugated louver fin 24 foreffecting heat exchange with air is provided between the adjacent flattubes 12, 12. The fin 24 is joined at left and right sides thereof tothe flat surfaces of the plates 2, 2.

[0081] The corrugated louver fin 24 has louvers formed simultaneouslywith bending for improved heat transfer.

[0082] The bottom of the U-shaped notch 14 formed in the widthwisemidportion of the upper end of each plate 2 needs to be positioned belowthe connecting portion 22 of the spectacle-shaped header member 20 so asto drain condensation water collecting in the notch.

[0083] Tacks 13, 13 for temporarily holding the header member 20 areprovided at the midportions of the lower edges defining the respectiveinlet-outlet through holes 10, 10 in the upper end of the plate 2. Theheader member 20 can be prevented from shifting by these tacks 13, 13during brazing.

[0084] With reference to FIGS. 1 and 4, a pair of side plates 25, 25 arearranged respectively at left and right ends of the evaporator 1. Theleft side plate 25 of the pair is provided with an inlet-outlet pipeconnecting block 27 joined to the upper end thereof. The side plate 25has a pair of front and rear through holes 26, 26 formed in the upperend thereof and communicating respectively with a pair of front and rearthrough holes 28, 28 formed in the block 27. The holes 26, 26 of theside plate 25 communicate respectively with the tube portions 21, 21 ofthe header member 20.

[0085] Incidentally, the side plate 25 need not be provided in the casewhere the block 27 is attached directly to the plate 2 at the left orright outer end of the evaporator 1. The block 17 may alternatively beprovided at an intermediate portion of the height of the side plate 25.The block 27 may further be provided at the midportion of length of theevaporator 1, or may comprise an inlet pipe connecting block and anoutlet pipe connecting block which are provided respectively at the leftand right ends of the evaporator so as to position an inlet and anoutlet individually at the left and right ends.

[0086] The evaporator components described are assembled and thereafterjoined together by brazing to fabricate the essential portion of theevaporator 1.

[0087] The assembly is brazed in a vacuum, or in a furnace with use of afluorine-containing flux.

[0088] It is desirable to use a material of relatively high strength forthe header member 20 and the side plates 25 in view of pressureresistance. It is especially desirable to use an aluminum alloycontaining magnesium added thereto.

[0089] In the case where the fluorine-containing flux is used, it isdesirable to use an aluminum alloy material having a magnesium contentpreferably of up to 0.4% since this results in improvements inbondability and strength.

[0090] The surfaces of the plate 2 and the corrugated fin 24 areapproximately flat so that the fin 24 can be joined to the flat tube 12nearly 100% to achieve highly efficient heat exchange between theinterior of the circuit of flat tubes 12 and the corrugated fins 24.

[0091] The header member 20 providing the headers 23, 23 has a generallyspectacle-shaped section with two refrigerant channels, one of which hasthe function of collecting or distributing an incoming portion ofrefrigerant, with the other serving to collect or distribute an outgoingportion of refrigerant.

[0092] When the heat exchanger of the present invention is used as anevaporator 1, the refrigerant is introduced into the flat tubes 12 inthe form of a mixture of a liquid and a gas. At this time, the liquidrefrigerant has a higher density than the gas and is more readilysubjected to an inertial force. The liquid refrigerant has higherproperties to advance straight than the gas. For this reason, the liquidrefrigerant tends to collect in a greater amount at a header end remotefrom the inlet header. An uneven flow of the liquid refrigerant upsetsthe balance of latent heat of vaporization in various portions,contributing greatly to impairment of performance. This can be precludedeffectively by causing the flat tube 12 to project into the header 23 toserve as a baffle and diminish the properties of the liquid refrigerantto advance straight.

[0093] The present invention is adapted to readily provide a bafflestructure, for example, by making the height b1 of the through hole 10at the inlet side of the flat tube 12 smaller than the inside diameterb2 of the refrigerant passing tube portion 21 of the header member 20.The effect of a baffle is available alternatively by reducing the crosssectional area of the front and rear tube portions 21 of the headermember 20 at one location or at a plurality of locations and therebyproducing flows of varying cross sectional areas.

[0094] Such a procedure diminishes the property of the liquidrefrigerant of advancing straight through the headers 23, 23, permittingthe refrigerant to flow into the flat tubes 12 in equally dividedquantities.

[0095] When the percentage of projection of the flat tube 12 into theheader 23 in the evaporator 1 of the invention is defined as:

(b2−b1)/b2

[0096] wherein b1 is the height of the through hole 10 at the inlet sideof the flat tube 12, and b2 is the inside diameter of the tube portion21 of the header member 20, the percentage of projection is in the rangeof 10 to 60% to be suitable. If the percentage of projection is lessthan 10%, no effect of baffle plate is available, readily permittingoccurrence of an uneven flow, whereas if the percentage of projection isover 60%, the header 23 offers increased resistance to the flow toentail impaired performance undesirably.

[0097] As shown in detail in FIG. 5, it is especially desirable that theU-shaped divided refrigerant passageways 7 formed in the refrigerantchannel 8 in the interior of each flat tube 12 be made generallyhexagonal in cross section by tapering the peripheral ridges 3, 3 on thepair of the plates 2, 2 of the tube 12 toward inward, tapering thecentral ridges 4, 4 thereon inward and tapering the channel dividingridges 5, 5 inward. The reason is that it is advantageous to spread theliquid refrigerant into a thin layer over the inner surface of therefrigerant channel 8 of the flat tube 12 for heat transfer.

[0098] Among the U-shaped divided refrigerant passageways 7 formed inthe channel 8 inside the flat tube 12, the passageway 7 a between theperipheral ridge 3 and the channel dividing U-shaped ridge 5 has ahexagonal cross section with a large width, and the passageways 7 bbetween the ridges 5, 5 have a hexagonal cross section with a smallwidth.

[0099] On the other hand, when the U-shaped divided refrigerantpassageways 7 formed in the inside refrigerant channel 8 of the flattube 12 have a rectangular cross section, for example, as shown in FIG.7, the liquid refrigerant is liable to collect in wall corners of theflat tube 12 if the circuit width is diminished to give an increasedsurface area to the refrigerant because the liquid refrigerant whichflows at a lower rate than the gas is forced toward the passageway ends.With the liquid refrigerant required for evaporation forced toward endportions, the liquid refrigerant will not adhere to the inner walls ofthe peripheral ridges 3, 3, central ridges 4, 4 and channel dividingridges 5, 5 in the flat tube 12 and will not be subjected to effectiveheat exchange, so that the heat exchanger fails to exhibit the desiredperformance.

[0100] When the divided refrigerant passageways 7 are made generallyhexagonal in cross section as seen in FIG. 5, the liquid refrigerantcollects in the recessed parts of intermediate portions of thepassageways 7 with the greatest ease, adhering to the tapered surfacesof the peripheral ridges 3, 3, those of the central ridges 4, 4 andthose of the dividing ridges 5, 5 on the pair of plates 2, 2 foreffective heat transfer and enabling these ridges to act effectively asinterior fins to exhibit improved heat transfer performance. As aresult, the heat transfer portions in the interior of the refrigerantpassageways 7 are increased in the area of effective parts to cool airto assure comfort.

[0101] However, the evaporator 1 of the invention may be so shaped asshown in either one of FIGS. 5 and 7 because the entire width of thechannel for passing cold refrigerant is equal to the width of contact ofthe corrugated fin 24 for the heat exchanger of the invention to achievea higher heat exchange efficiency than the conventional one.

[0102] According to the first embodiment of the invention described, theplate 2 is, for example, 10 to 40 mm in width and 0.25 to 1.0 mm inthickness.

[0103] The peripheral ridge 3 on the plate 2 is, for example, 0.25 to1.0 mm in thickness and 0.5 to 2.0 mm in width. The central ridge 4 onthe plate 2 is, for example, 0.25 to 1.0 mm in thickness and 0.5 to 2.0mm in width. The channel dividing U-shaped ridge 5 on the plate 2 is,for example, 0.25 to 1.0 mm in thickness and 0.25 to 1.0 mm in width.

[0104] With the evaporator 1 described above, the refrigerant introducedinto the front header 23 through one of the through holes 28, i.e., theinlet hole 28, in the pipe connecting block 27 flows into dividedrefrigerant passageways 7 from one end of the U-shaped refrigerantchannel 8 of each flat tube 12, flows through the U-shaped passageways 7to the other end of the channel 8, further passes through the rearheader 23 and the other through hole 28, i.e., the outlet hole 28, inthe block 27 and flows out of the evaporator.

[0105] On the other hand, air flows through the evaporator 1 from thefront rearward through the spaces each having the corrugated louver fin24 therein and formed between the adjacent flat tubes 12 and between thetube 12 and each end plate 25 to undergo efficient heat exchange withthe refrigerant through the walls of the flat tube 12, the end plates 25and the louver fins 24.

[0106] The evaporator 1 according to the first embodiment is fabricatedfrom plates which have recesses and ridges formed on one side thereof asby forging or cutting and which are used in place of conventional platesformed by press work. The front and rear headers are formed by headermembers which are separate from the plates. These features give the flattubes 12 a reduced front-to-rear width and a decreased thickness(thinner layers) and afford a greater area of heat transfer, enablingthe evaporator to achieve a higher heat transfer efficiency and exhibitgreatly improved heat exchange performance.

[0107] To assure the refrigerant of improved heat transfer in the flattube 12, it is desired that a plurality of cutouts 15 be formed in thechannel dividing U-shaped ridges 5 on each plate 2 at a predeterminedspacing, for example as shwon in FIG. 8, the cutouts 15 in the adjacentridges 5 being in a staggered arrangement, so as to cause the dividedadjacent refrigerant passageways 7, 7 in the interior of the tube 12 tocommunicate with each other through the cutouts 15.

[0108] Alternatively, the flat tube 12 may have turbulence promotingmembers (projections) 16 in a staggered arranged for producing turbulentflows of refrigerant for improved heat transfer, for example, as shownin FIGS. 9 and 10.

[0109]FIGS. 11 and 12 show a second embodiment of the invention. Thisembodiment differs from the first in that a pair of front and rearheader members 41, 42 each in the form of a pipe having a rectangularcross section are used.

[0110] Stated more specifically, an evaporator 1 is fabricated fromgenerally rectangular plates 2 which are aluminum plates. Each of theseplates 2 has an edge ridge 33 provided on one side of the plate alongopposite side edges and a lower edge thereof and U-shaped in itsentirety, and a central ridge 34 provided on the same side of the plate2 at the center of the width thereof and having a bifurcated upper end34 a, the central ridge 34 extending from the upper end 34 a downward toa position where a refrigerant return channel can be formed. The plate 2has a U-shaped refrigerant channel recess 36 formed internally of theU-shaped edge ridge 33 and comprising front and rear straightrefrigerant channel recess portion 36 a, 36 a formed on opposite sidesof the central ridge 34 and a refrigerant return channel recess portion36 c positioned under the central ridge. The plate 2 has a plurality ofchannel diving U-shaped ridges 35 formed inside the channel recess 36and extending over the approximate entire length thereof.

[0111] The corners of return channel recess portion 36 c of the channelrecess 36 has short circular-arc ridges 39 for achieving an improvedheat exchange efficiency at the corner portions.

[0112] According to this second embodiment, the plate 2 is provided inthe widthwise midportion of its upper end with a notch 37 which isU-shaped when seen from the front. The central ridge 34 has thebifurcated upper end 34 a.

[0113] Each plate 2 is formed, for example, by forging or cutting.Plates 2 are provided in pairs, and each pair of plates 2 are fittedtogether with their U-shaped channel recesses 36, 36 opposed to eachother to join the opposed U-shaped edge ridges 33, 33 of the plates 2, 2to each other end-to-end, the opposed central ridges 34, 34 includingthe bifurcated upper ends 34 a to each other end-to-end and each of theopposed pairs of channel dividing rides 5, 5 each other end-to-end andto thereby form a flat tube 32 having upper ends 32 a, 32 a which arebifurcated and opened, with a plurality of U-shaped divided refrigerantpassageways formed inside the flat tube 32.

[0114] On the other hand, a pair of front and rear header members 41, 42are each in the form of a pipe rectangular in cross section and having alower wall 43, front wall 45, rear wall 46 and upper wall 47. The headermembers 41, 42 have slits 44, 44 formed in the respective lower walls43, 43 thereof and arranged at a predetermined spacing. Flat tubes 32are arranged in parallel laterally, with a front and a rear headerprovided in communication with the bifurcated open upper ends 32 a, 32 aof the flat tubes 32, by inserting the bifurcated open upper ends 32 a,32 a thereof into the respective slits 44, 44 of the juxtaposed headermembers 41, 42 and thereby joining the flat tubes to the header members.At this time, the rear wall 46 and the front wall 45 of the respectivejuxtaposed front and rear header members 41, 42 are fitted as joinedtogether into U-shaped notches 37, 37 in the upper ends of the opposedplates 2, 2 of each flat tube 32.

[0115] Below the headers, a corrugated fin 24 is provided between theadjacent flat tubes 32, 32. The fin 24 is joined at left and right sidesthereof to the flat surfaces provided by the other sides of the plates2, 2.

[0116] The evaporator 1 of the second embodiment is fabricated in thesame manner as the first in that the assembly of components is brazed ina vacuum, or in a furnace with use of a fluorine-containing flux, sothat throughout the drawings concerned, like parts are designated bylike reference numerals.

[0117] Although not shown, the pair of front and rear header members 41,42 each in the form of rectangular pipe may be replaced by a singlealuminum extrudate having two refrigerant channels generally rectangularin cross section and partitioned by a central wall for use in theevaporator 1 according to the second embodiment described. The extrudatehas slits 44, 44 formed in the respective portions of a lower wallthereof which define the refrigerant channels and arranged at apredetermined spacing. A front and a rear header are provided incommunication with the bifurcated open upper ends 32 a, 32 a of thejuxtaposed flat tubes 32 by inserting the bifurcated open upper ends 32a, 32 a the tubes into the respective slits 44, 44 and thereby joiningthe tubes to the lower wall.

[0118] FIGS. 13 to 17 show a third embodiment of the present invention,which differs from the first in that headers 57 and headers 58 areprovided respectively at the top and bottom of an evaporator 1.

[0119] With reference to these drawings, a generally rectangular plate 2made of an aluminum plate has a peripheral ridge 3 provided on one sideof the plate 2 along a periphery thereof and a central ridge 4 providedon the same side of the plate 2 at the center of the width thereof andextending vertically. Formed in the plate 2 internally of the peripheralridge 3 are front and rear refrigerant channel recess portions 6 a, 6 bpositioned on opposite sides of the central ridge 4 and through holes10, 10 formed in the upper and lower ends of the recess portions 6 a, 6b. The plate 2 has straight channel diving ridges 5 formed inside thechannel recess portions 6 a, 6 b and extending over the approximateentire length of the portions 6 a, 6 b.

[0120] The plate 2 is formed, for example, by forging or cutting. Suchplates 2 are provided in pairs, and each pair of plates 2 are fittedtogether with their recess portions 6 a, 6 b opposed to each other tojoin the opposed peripheral ridges 3, 3 of the plates 2, 2 to each otherend-to-end, the opposed central ridges 4, 4 thereof to each otherend-to-end and each of the opposed pairs of channel dividing rides 5, 5to each other end-to-end and to thereby form a flat tube 12 having aU-shaped refrigerant channel 8 inside thereof, with parallel dividedrefrigerant passageways 7 formed in the inside the flat tube 12 (seeFIG. 7 of the first embodiment).

[0121] A required number of flat tubes 12 are arranged side by side.Spectacle-shaped upper and lower header members 51, 52, each comprisinga pair of front and rear refrigerant passing tube portions 53, 53 or 54,54 and a connecting portion 55 or 56 therebetween, are interposedrespectively between the upper ends of each pair of adjacent flat tubesand between the lower ends thereof, the tube portions 53 or 54 being incommunication with the corresponding through holes 10 of the opposedplates 2.

[0122] As shown in detail in FIG. 14, of the pairs of front and rearthrough holes 10, 10 formed in the upper and lower ends of the plate 2,the pair of front and rear through holes 10 a, 10 a in the upper end ofthe plate 2 are each in the form of a circle which is elongatedhorizontally. In corresponding relation with these holes, the front andrear tube portions 53, 53 of the upper header member 51 provided betweenthe upper ends of the flat tubes 12, 12 have a circular cross sectionwhich is similarly elongated horizontally. On the other hand, the pairof front and rear through holes 10 b, 10 b in the lower end of the plate2 are each in the form of a circle which is elongated as inclinedforwardly downward or rearwardly downward. In corresponding relationwith these holes, the front and rear tube portions 54, 54 of the lowerheader member 52 provided between the lower ends of the flat tubes 12,12 have a circular cross section which is similarly elongated asinclined forwardly downward or rearwardly downward.

[0123] With reference to FIGS. 16 and 17, opposite end faces of the tubeportions 53, 53 and 54, 54 of the upper and lower header members 51, 52are joined to flat surfaces on the other sides of the plates of the flattubes 12, 12 which surfaces are opposed to the end faces, whereby upperand lower headers 57, 58 are formed in communication respectively withthe upper ends and lower ends of the flat tubes 12, 12.

[0124] Between the upper and lower headers 57, 58, a corrugated louverfin 24 for effecting heat exchange with air is interposed between eachpair of adjacent flat tubes 12, 12. The fin 24 is joined at oppositeside edges thereof to the other sides, i.e., the flat surfaces of theplates 2, 2 of the flat tubes 12, 12.

[0125] Of the upper and lower header members 51, 52 between the adjacentflat tubes 12, 12 in the evaporator 1 of the third embodiment, the lowerheader member 52 has passages 59, 59 formed at opposite sides of theintermediate connecting portion 56 for interconnecting the front andrear tube portions 54, 54 of the header member 52.

[0126] With the evaporator 1 of the third embodiment described, therefrigerant is introduced from an inlet through hole 18 in aninlet-outlet pipe connecting block 27 into the front tube portion 53 ofeach upper header member 51 providing the front upper header 57, fromwhich the refrigerant flows into the front upper end of refrigerantchannel 8 of each flat tube 12, further flows down the straight dividedrefrigerant passageways 7 to reach the front lower end of the channel 8,from which the refrigerant temporarily flows into the front tube portion54 of the lower header member 52 providing the front lower header 58,then passes through the interconnecting passages 59, 59 in the lowerheader member 52 and flows into the rear tube portion 54 providing therear lower header 58. Subsequently, the refrigerant flows into the rearlower end of the refrigerant channel 8 of the flat tube 12, furtherascends the straight divided refrigerant passageways 7 to reach the rearupper end of the channel 8, passes through the rear tube portion 53 ofthe upper header member 51 providing the rear upper header 57 and flowsout of an outlet through hole 28 in the block 27.

[0127] With the evaporator 1 of the third embodiment, the front and reartube portions 54, 54 of the lower header member 52 between the lowerends of the flat tubes 12, 12 have a circular cross section which iselongated as inclined forwardly downward or rearwardly downward so as tocause the water produced upon condensation on the outer surface of theevaporator 1 during due to be drained smoothly.

[0128] Although not shown, the evaporator 1 of the third embodiment mayalso be modified like the modification of FIG. 8, by forming a pluralityof cutouts 15 in the channel dividing ridges 5 on each plate so that theadjacent divided refrigerant passageways 7, 7 inside the flat tube 12communicate with each other through the cutouts 15.

[0129] Of the upper and lower header members 51, 52 provided between theadjacent flat tubes 12, 12 at their upper ends and lower ends in theevaporator 1 of the third embodiment, the upper header member 51 mayhave passages 59, 59 formed at opposite sides of the intermediateconnecting portion 55 for interconnecting the front and rear tubeportions 53, 53 of the header member 51, in converse relation with theillustrated case so as to cause the refrigerant to flow in the oppositedirection to the illustrated case.

[0130] The evaporator 1 of the third embodiment otherwise has the sameconstruction as the first embodiment described, so that like parts aredesignated by like reference numerals throughout the drawings concerned.

[0131]FIGS. 18 and 19 show a second modification of channel dividingridges 5 on the plate 2 for use in the evaporator according to the firstembodiment of the invention, i.e., channel dividing ridges 5 a, 5 bformed in the refrigerant channel recess 6 of each plate 2, which differfrom the channel dividing U-shaped ridges 5 shown in FIGS. 2, 3 and 5showing the first embodiment in configuration and arrangement. Anotherdifference is that the ridges 5 a, 5 b on each plate 2 have top endsjoined to the flat bottom wall of the plate 2 opposed thereto andproviding the refrigerant channel recess 6 thereof.

[0132] With reference to FIGS. 18 and 19, each plate 2 of the evaporator1 has on one side thereof a peripheral ridge 3 along the peripherythereof and a central ridge 4 at the center of the width of the plateand extending downward from the upper end of the plate to a positionwhere a return channel can be formed. More specifically, each pair ofplates 2 a, 2 b have formed in a refrigerant channel recess 6 thereof amultiplicity of front and rear channel dividing ridges 5 a, 5 b having aheight twice the depth of the channel recess 6. These ridges 5 a, 5 bare so provided as to form independent parallel U-shaped dividedrefrigerant passageways 7 in a U-shaped refrigerant channel 8 of a flattube 12 when the pair of plates 2 a, 2 b are fitted together.

[0133] With reference to FIG. 18, these ridges 5 a, 5 b each comprise astraight portion 5 a 1 or 5 b 1 positioned in the front or rear straightchannel recess portion 6 a or 6 b of the refrigerant channel recess 6and a quarter circular-arc portion 5 a 2 or 5 b 2 extending from thestraight portion and positioned in the return portion 6 c of the recess6. The ridges 5 a, 5 b correspond to exactly half of a U-shape inconfiguration.

[0134] When the pair of plates 2 a, 2 b are fitted together with therecesses 6, 6 opposed to each other, the straight portions 5 a 1, 5 b 1and quarter circular-arcs 5 a 2, 5 b 2 of these ridges 5 a, 5 b arealternately arranged at a predetermined spacing.

[0135] With the pair of plates 2 a, 2 b fitted together, the opposedcentral ridges 4, 4 are butted against and joined to each other, withthe peripheral ridges 3, 3 similarly joined to each other, and thestraight portions 5 a 1, 5 b 1 and the quarter circular-arcs 5 a 2, 5 b2 of the channel dividing ridges 5 a, 5 b on each of the plates 2 a, 2 bare joined at their top ends to the bottom wall flat surface of theother plate 2 a or 2 b opposed thereto and providing the channel recess6, whereby a flat tube 12 is formed with a U-shaped refrigerant channel8 formed therein. In the channel 8 of the flat tube 12, the frontchannel dividing ridges 5 a on the plate 2 a of the pair 2 a, 2 b arejoined in a U-form to the rear ridges 5 b on the other plate 2 b,providing divided parallel U-shaped refrigerant passageways 7. Thedivided passageways 7 in the return portion are in the form ofsemicircular arcs.

[0136] The return channel recess portion 6 c of the U-shaped channelrecess 6 is provided at the corners on front and rear sides with shortcircular-arc ridges 9 a, 9 b to ensure improved heat exchangeperformance of this portion. These circular-arc ridges 9 a, 9 b are soarranged as to be positioned alternately at a predetermined spacing whenthe pair of plates 2 a, 2 b are fitted together with the recesses 6, 6thereof opposed to each other.

[0137] The above modification is the same as the first embodimentotherwise; for example, each plate 2 is made by forging or cutting.Throughout the drawings concerned, therefore, like parts are designatedby like reference numerals.

[0138] With the evaporator 1 described above, the front and rear channeldividing ridges 5 a, 5 b on the pair of plates 2 a, 2 b comprisestraight portions 5 a 1, 5 b 1 and quarter circular-arc portions 5 a 2,5 b 2 and are shaped to correspond to exactly half of a U-shape. Theseridges 5 a, 5 b are so arranged that when the pair of plates 2 a, 2 bare fitted together with the recesses 6, 6 opposed to each other, theridges 5 a, 5 b are positioned alternately at a predetermined spacing.Accordingly, the number of dividing ridges 5 a, 5 b to be made as byforging or cutting can be diminished, while the ridges 5 a, 5 b on theplates 2 a, 2 b can be spaced apart by an increased interval and can beshaped to have exactly half of the U-shape, hence the advantage that theplates 2 a, 2 b are easy to produce.

[0139]FIGS. 20 and 21 show a third modification of channel dividingridge 5 on the plate 2 for use in the evaporator 1 according to thefirst embodiment of the invention. The modification differs from thefirst embodiment in that two kinds of plates 2 a, 2 b have channeldividing U-shaped ridges 5 a, 5 b which are different in arrangement inrefrigerant channel recesses 6, 6, and that the ridges 5 a, 5 b on theplates 2 a, 2 b have their top ends joined to the bottom wall flatsurface of the recesses 6 of the plates 2 b, 2 a opposed thereto.

[0140] With reference to the same drawings, the channel dividingU-shaped ridges 5 a, 5 b having a height twice the depth of recesses 6,6 are provided in the U-shaped recesses 6, 6 of the pair of plates 2 a,2 b so as to be alternately positioned at a predetermined spacing whenthese plates 2 a, 2 b are fitted together face-to-face.

[0141] With these plates 2 a, 2 b fitted together face-to-face, theopposed central ridges 4, 4, as well as the opposed plate peripheralridges 3, 3, are butted against and joined to each other, and thechannel dividing U-shaped ridges 5 a, 5 b on the plates 2 a, 2 b havetheir top ends joined to the bottom wall flat surfaces of the recesses6, 6 of the plates 2 b, 2 a opposed thereto, whereby a flat tube 12 isformed which has parallel U-shaped refrigerant passageways 7 divided bythe ridges 5 a, 5 b and provided in the U-shaped refrigerant channel 8.

[0142] In the front and rear corners of the refrigerant return channelrecess portions 6 c of the U-shaped refrigerant channel recesses 6, 6,short circular-arc ridges 9 a, 9 b are provided for these portions toexhibit improved heat exchange performance. These front and rear shortcircular-arc ridges 9 a, 9 b are alternately positioned at apredetermined spacing when the pair of plates 2 a, 2 b are fittedtogether face-to-face.

[0143] The above modification is the same as the first embodimentotherwise; for example, each plate 2 is made by forging or cutting.Throughout the drawings concerned, therefore, like parts are designatedby like reference numerals.

[0144] With the evaporator 1 wherein the two kinds of plates 2 a, 2 bare used, the channel dividing U-shaped ridges 5 a, 5 b on the twoplates 2 a, 2 b are so arranged that when these plates 2 a, 2 b arefitted together face-to-face, the ridges 5 a, 5 b are positionedalternately at a predetermined spacing. Accordingly, the number ofdividing ridges 5 a, 5 b to be made as by forging or cutting can besmaller, while the ridges 5 a, 5 b on the plates 2 a, 2 b can be spacedapart by an increased interval, hence the advantage that the plates 2 a,2 b are easy to produce.

[0145]FIGS. 22 and 23 show a fourth modification of channel dividingridge 5 on the plate 2 for use in the evaporator 1 according to thefirst embodiment of the invention. The modification differs from thefirst embodiment in that a multiplicity of channel dividing ridges 5 areprovided only in the rear half of the refrigerant channel recess 6 ofeach plate 2, with no ridges 5 whatever provided in the front half ofthe recess 6 and with the front half made flat-surfaced, in that theridges 5 are shaped to have exactly half of a U-shape, and in that theridges 5 on each plate 2 have their top ends joined to the bottom wallflat surface of the recess 6 of the other plate 6 opposed thereto.

[0146] With reference to the same drawings, each plate 2 of theevaporator 1 has a peripheral ridge 3 provided on one side of the platealong a periphery thereof and a central ridge 4 provided on the sameside of the plate at the center of the width thereof and extendingdownward from an upper end of the plate to a position where a returnchannel can be formed. A multiplicity of channel dividing ridges 5 bhaving a height twice the depth of the recess 6 are provided in the rearhalf of the refrigerant channel recess 6 of each plate 2, with no ridges5 whatever provided in the front half of the recess 6 and with the fronthalf made flat-surfaced.

[0147] Stated more specifically with reference to FIG. 22, the channeldividing ridges 5 b provided in the rear half of the refrigerant channelrecess 6 of each plate 2 each comprise a straight portion 5 b 1 formedin a rear straight channel recess portion 6 b and a quarter circular-arcportion 5 b 2 extending from the straight portion and provided in areturn portion 6 c of the recess 6, the ridges 5 b being shaped to haveexactly half of a U-shape.

[0148] With a pair of plates 2 a, 2 b fitted together face-to-face, theopposed central ridges 4, 4, as well as the opposed plate peripheralridges 3, 3, are butted against and joined to each other, and thechannel dividing U-shaped ridges 5, 5 on the plates 2 a, 2 b have theirtop ends joined to the bottom wall flat surfaces of the refrigerantchannel recesses 6, 6 of the plates 2 b, 2 a opposed thereto, whereby aflat tube 12 is formed which has a U-shaped refrigerant channel 8. Thefront ridges 5 a on one plate 2 a of the two 2 a, 2 b are madecontinuous with the rear ridges 5 b on the other plate 2 b, wherebyparallel U-shaped divided refrigerant passageways 7 are formed in theU-shaped refrigerant channel 8 of the flat tube 12. The passageways 7have semicircular-arc return portions.

[0149] Short circular-arc ridges 9 are provided on the rear cornerportion of the return channel recess portion 6 c of the recess 6 forthis portion to exhibit improved heat exchange performance.

[0150] The above modification is the same as the first embodimentotherwise; for example, each plate 2 is made by forging or cutting.Throughout the drawings concerned, therefore, like parts are designatedby like reference numerals.

[0151] With the evaporator 1, the channel dividing ridges 5 on eachplate 2 each comprise a straight portion 5 b 1 and a quartercircular-arc portion 5 b 2 extending therefrom and are shaped to haveexactly half of a U-shape, while the front half of the recess 6 of eachplate 2 has a flat surface provided with no channel dividing ridges 5.Accordingly, the ridges 5 to be formed on the plate 2 as by forging orcutting can be half, hence the advantage that the plates 2 a, 2 b areeasy to make.

[0152]FIG. 24 shows a pair of plates for use in the evaporator 1 of thefirst embodiment of the invention, with one of the plates replaced by aflat plate.

[0153] With reference to the drawing, the ridged plate 2 of the firstembodiment, i.e., the plate 2 b comprises, as will be apparent from FIG.2, a peripheral ridge 3 provided on one side of the plate along aperiphery thereof and a central ridge 4 provided on the same side of theplate at the center of the width thereof and extending downward from theupper end of the plate to a position where a refrigerant return channelcan be formed. Formed in the plate internally of the peripheral ridge 3is a U-shaped refrigerant channel recess 6 comprising front and rearstraight refrigerant channel recess portions 6 a, 6 b positioned onopposite sides of the central ridge 4 and a refrigerant return channelrecess portion 6 c positioned under the central ridge. The plate has aplurality of channel diving U-shaped ridges 5 formed inside the channelrecess 6 and extending over the approximate entire length thereof. Theplate 2 b is provided in the widthwise midportion of its upper end witha notch 14 which is U-shaped when seen from the front. The central ridge4 is joined at its upper end to the peripheral ridge 3 at the lower endof this notch 14. The channel recess 6 of the plate 2 b has one ofrefrigerant inlet-outlet through holes 10, 10 formed at one end thereofand the other through hole 10 formed at the other end thereof.

[0154] The flat plate 2 a, on the other hand, has no U-shaped recess norany channel dividing U-shaped ridge but has a flat surface and the samecontour as the ridge plate 2 b. The plate 2 a is provided at thewidthwise midportion of its upper end with a notch which is U-shapedwhen seen from the front. The flat plate 2 a further has refrigerantinlet-outlet through holes formed in its upper end at front and rearsides thereof (not shown).

[0155] Such flat plates 2 a and ridged plates 2 b are provided in pairs,with each pair of plates fitted together face-to-face. The peripheralridge 3 on the ridged plate 2 b has its top end joined to the flatsurface of the peripheral edge portion of the flat plate 2 a, with thetop end of the central ridge 4 joined to the flat surface of the centralportion of the flat plate 2 a, and with the top ends of the ridges 5joined to the corresponding flat surface portions of the flat plate 2 a,whereby a flat tube 12 is formed which has a U-shaped refrigerantchannel 8, with a plurality of divided refrigerant passageways 7 formedin the channel 8.

[0156] The evaporator 1 comprising flat plates 2 a described is the sameas the first embodiment otherwise; for example, the ridged plate 2 b ismade as by forging or cutting. Throughout the drawings concerned,therefore, like parts are designated by like reference numerals.

[0157] The evaporator 1 comprises ridged plates 2 b having a peripheralridge 3, central ridge 4 and channel dividing ridges 5, and flat plates2 a-having the same contour as the plate 2 b. This serves to halve thenumber of ridged plates 2 b used which are prepared as by forging orcutting, consequently entailing the advantage of making the evaporator 1easy to fabricate.

[0158] The evaporator 1 can be modified as will be described below whichis the second embodiment of the invention shown in FIGS. 11 and 12 andwherein a pair of front and rear header members 41, 42 used are each inthe form of a pipe of rectangular cross section.

[0159] Like the modification shown in FIGS. 18 and 19, the first ofmodifications has a multiplicity of channel diving ridges 5 a, 5 bformed in the channel recess 6 of each plate 2, comprising straightportions 5 a 1, 5 b 1 and quarter circular-arc portions 5 a 2, 5 b 2extending therefrom, and having exactly half of a U-shape and a heighttwice the depth of the recess 6. When a pair of plates 2 a, 2 b arefitted together face-to-face, a flat tube 12 is formed wherein theridges 5 a, 5 b form independent parallel U-shaped divided refrigerantpassageways 7 in a U-shaped refrigerant channel 8. The ridges 5 a, 5 bof each plate 2 have their top ends joined to the bottom wall flatsurface of the recess 6 of the other plate 2 opposed to the ridges. Likethe modification shown in FIGS. 20 and 21, two kinds of plates 2 a, 2 bcan be used in the second modification to be described below. The plates2 a, 2 b have channel dividing U-shaped ridges 5 a, 5 b which aredifferent in arrangement in refrigerant channel recesses 6, 6, and havea height twice the depth of the recesses 6, 6. In this case, the ridges5 a, 5 b on each of the plates 2 a, 2 b have their top ends joined tothe bottom wall flat surface of the recesses 6 the other of these plates2 b, 2 a opposed thereto.

[0160] As is the case with the embodiment shown in FIGS. 22 and 23,usable in a third modification are plates 2 which have a multiplicity ofchannel dividing ridges 5 formed only in the rear half of therefrigerant channel recess 6. The front half of the recess 6 has noridges whatever and is flat-surfaced. In this case, the ridges 5 on eachplate 2 have their top ends joined to the bottom wall flat surface ofthe recess 6 of the other plate 2 opposed thereto.

[0161] As is the case with the flat tube shown in FIG. 24, usable in afourth modification in combination with a ridged plate 2 b which is theplate 2 of the second embodiment of FIG. 12 is a flat plate 2 a havingthe same contour as the plate 2 b. In this case, the peripheral ridge 3on the ridged plate 2 b has its top end joined to the flat surface ofthe peripheral edge portion of the flat plate 2 a, with the top end ofthe central ridge 4 joined to the flat surface of the central portion ofthe flat plate 2 a and with the top ends of the channel dividing ridges5 joined to the corresponding flat surface portions of the flat plate 2a, whereby a flat tube 12 is provided wherein a plurality of U-shapeddivided refrigerant passageways 7 are formed in a refrigerant channel 8.

[0162] Although not shown, the evaporator 1 of the third embodiment ofthe invention wherein the upper and lower headers 57, 58 are providedmay comprise the pair of front and rear header members 41, 42 each inthe form of a rectangular pipe and shown in FIGS. 11 and 12, in place ofthe spectacle-shaped upper and lower header members 51, 52 shown inFIGS. 16 and 17.

[0163] The evaporator thus modified will be referred to a fourthembodiment of the invention. The evaporator 1 according to the fourthembodiment of the invention will be described using reference numeralsof FIGS. 11 and 12. Each of plates 2 in pairs has straight side edgeridges 33, 33 provided on one side of the plate along opposite sideedges thereof and a central ridge 34 provided on the same side of theplate at the center of the width thereof and having bifurcated upper andlower ends 34 a, 34 a, the ridges being formed by forging or cutting,each plate 2 having front and rear straight channel recess portions 36a, 36 a formed inwardly of the side edge ridges on opposite sides of thecentral ridge 34, each plate 2 having a flat surface on the other sidethereof, each of the pairs of plates being fitted together with theirfront and rear channel recess portions 36 a, 36 b opposed to each otherto join the opposed straight side edge ridges 33, 33 to each otherend-to-end and the opposed central ridges 34, 34 including thebifurcated upper and lower ends 34 a, 34 a to each other end-to-end andto thereby form a flat tube 32 having bifurcated open upper and lowerends and front and rear straight fluid channels 38, 38 inside thereof,an upper and a lower pair of front and rear header members 41, 42 beingeach in the form of a pipe having a rectangular cross section, each ofthe header members 41, 42 having slits 44, 44 formed in an upper wall 47or a lower wall thereof 43 and arranged at a predetermined spacing, aplurality of flat tubes 32 being arranged in parallel by inserting thebifurcated upper or lower ends thereof into the respective slits 44, 44in the header members 41, 42 to join the flat tubes to the headermembers and to provide an upper and a lower pair of front and rearheaders in communication with the bifurcated upper and lower ends of theflat tubes 32 respectively. At this time, the rear wall 46 and the frontwall 45 of the respective juxtaposed front and rear header members 41,42 are fitted as joined together into U-shaped notches 37, 37 in theupper ends of the opposed plates 2, 2 of each flat tube 32.

[0164] Described below are modifications of the evaporator 1 of thethird embodiment of the invention wherein the upper and lower headers57, 58 are provided by the spectacle-shaped upper and lower headermembers 51, 52 and the evaporator 1 of the fourth embodiment of theinvention wherein the upper and lower headers are provided by pairs offront and rear header members 41, 42 in the form of rectangular pipes.

[0165] Like the embodiment shown in FIGS. 18 and 19, usable for a firstmodification are plates 2, 2 a, 2 b each having formed in respectivefront and rear refrigerant channel recess portions 6 a, 6 b thereof manyfront and rear channel dividing ridges 5 a, 5 b having a height twicethe depth of the recess portions 6 a, 6 b. These ridges 5 a, 5 b are soprovided as to form parallel divided independent refrigerant passageways7 in a refrigerant channel 8 in a flat tube 12 when each of pairs ofplates 2 a, 2 b are fitted together face-to-face. In this case, thechannel dividing ridges 5 a, 5 b of each of the plates 2 a, 2 b havetheir top ends joined to the bottom wall flat surface of recess portions6 a, 6 b of the other plate 2 a or 2 b opposed thereto.

[0166] Like the embodiment shown in FIGS. 20 and 21, two kinds of plates2 a, 2 b are usable for a second modification. These plates 2 a, 2 b aredifferent in the arrangement of straight channel dividing ridges 5 a, 5b which are provided in refrigerant channel recesses 6, 6 and which havea height twice the depth of the recesses 6, 6. In this case, thestraight channel dividing ridges 5 a, 5 b on each of the plates 2 a, 2 bhave their top ends joined to the bottom wall flat surface of recessportion of the other plate 2 a or 2 b opposed thereto.

[0167] As is the case with the embodiment shown in FIGS. 22 and 23,usable in a third modification are plates 2 which have a multiplicity ofchannel dividing straight ridges 5 formed only in the rear half of therefrigerant channel recess 6. The front half of the recess 6 has noridges whatever and is flat-surfaced. In this case, the straight ridges5 on one plate 2 have their top ends joined to the bottom wall flatsurface of the recess 6 of the other plate 2 opposed thereto.

[0168] As in the case of the flat tube shown in FIG. 24, usable in afourth modification in combination with a ridged plate 2 b is a flatplate 2 a having the same contour as the plate 2 b. In this case, theside edge ridges 3, 33 on the ridged plate 2 b have their top endsjoined to the flat surface of the side edge portions of the flat plate 2a, with the top end of the central ridge 4, 34 joined to the flatsurface of the central portion of the flat plate 2 a and with the topends of the channel dividing straight ridges 5 joined to thecorresponding flat surface portions of the flat plate 2 a, whereby aflat tube 12, 32 is provided which has front and rear straightrefrigerant channel 8, 38 formed in the tube and a plurality of dividedrefrigerant passageways 7 formed in the refrigerant channel 8, 38.

[0169] Although the heat exchanger 1 of the present invention has beendescribed with reference to embodiments for use as evaporators for motorvehicle air conditioners, the present invention can be applied also toheat changers for use in motor vehicles or in industries, such asevaporators, condensers, oil coolers, intercoolers, heater cores, etc.

[0170] In the case where the heat exchanger 1 of the invention is to beused, for example, as a heater heat exchanger for heating systems,efficient heat exchange is available since the entire width of thechannel for the fluid is equal to the contact width of the radiator fin24. Furthermore, the internal fluid can be passed in a counterflowrelation with air. This results in an increased temperature efficiencyto achieve higher heat exchanger effectiveness and realize a compacteddevice.

1. A heat exchanger comprising pairs of plates with each plate of thepairs having a peripheral ridge provided on one side of the plate alonga periphery thereof and a central ridge provided on said one side of theplate at a center of the width thereof and extending downward from anupper end of the plate to a position where a return channel can beformed, the ridges being formed by forging or cutting, each plate ofsaid pairs having a U-shaped channel recess formed inwardly of theperipheral ridge and comprising a front and a rear channel recessportion formed on opposite sides of the central ridge and a returnchannel recess portion positioned under the central ridge, the channelrecess having one of two fluid inlet-outlet through holes formed at oneend thereof and the other through hole formed at the other end thereof,each plate of said pairs having a flat surface on the other sidethereof, each of said pairs of plates being fitted together with theirU-shaped channel recesses opposed to each other to join the opposedperipheral ridges to each other end-to-end and the opposed centralridges to each other end-to-end and to thereby form a flat tube having aU-shaped fluid channel inside thereof so that a plurality of flat tubesare arranged in parallel with a header member interposed between upperends of each pair of adjacent flat tubes to provide a front and a rearheader in communication with the upper ends of the said pair of adjacentflat tubes, the header member comprising a pair of front and rear fluidpassing tube portions in communications with the respective inlet-outletthrough holes of the plates of said pair of adjacent flat tubes and aconnecting portion between the tube portions.
 2. A heat exchangercomprising pairs of plates with each plate of the pairs having an edgeridge U-shaped in its entirety and provided on one side of the platealong opposite side edges and a lower edge thereof and a central ridgeprovided on said one side of the plate at a center of the width thereofand having a bifurcated upper end, the central ridge extending from theupper end downward to a position where a return channel can be formed,the ridges being formed by forging or cutting, each plate of said pairshaving a U-shaped channel recess formed inwardly of the U-shaped edgeridge and comprising a front and a rear channel recess portion formed onopposite sides of the central ridge and a return channel recess portionpositioned under the central ridge, each plate of said pairs having aflat surface on the other side thereof, each of said pairs of platesbeing fitted together with their U-shaped channel recesses opposed toeach other to join the opposed U-shaped edge ridges to each otherend-to-end and the opposed central ridges including the bifurcated upperends to each other end-to-end and to thereby form a flat tube havingbifurcated open upper ends and a U-shaped fluid channel inside thereof,a pair of front and rear header members being each in the form of a pipehaving a rectangular cross section, each of the header members havingslits formed in a lower wall thereof and arranged at a predeterminedspacing, a plurality of flat tubes being arranged in parallel byinserting the bifurcated open upper ends thereof into the respectiveslits in the front and rear header members to join the flat tubes to theheader members and to provide a front and a rear header in communicationwith the bifurcated open upper ends of the flat tubes.
 3. A heatexchanger according to claim 1 or 2 wherein a plurality of channeldividing U-shaped ridges are formed in the U-shaped channel recess ofeach plate by forging or cutting, and each said pair of plates arefitted together with the recesses thereof opposed to each other and witheach of opposed pairs of channel dividing U-shaped ridges joined to eachother end-to-end to form a plurality of U-shaped divided fluidpassageways in the U-shaped fluid channel inside the flat tube.
 4. Aheat exchanger according to claim 1 or 2 wherein each plate of saidpairs has formed in the channel recess thereof front and rear channeldividing ridges having a height twice the depth of the channel recessand each comprising a straight portion positioned in the front or rearstraight channel recess portion of the channel recess and a quartercircular-arc portion extending from a lower end of the straight portionand positioned in the return portion of the channel recess, the channeldividing ridges being formed by forging or cutting and positionedalternately when each of said pairs of plates are fitted together withtheir channel recesses opposed to each other, each of said pairs ofplates being fitted together with their channel recesses opposed to eachother to join top ends of the front and rear channel dividing ridges toa bottom wall flat surface of the plate providing the channel recess andopposed thereto and to thereby form U-shaped divided fluid passagewaysin the U-shaped fluid channel inside the flat tube.
 5. A heat exchangeraccording to claim 1 or 2 wherein each plate of said pairs has formed inthe channel recess thereof channel dividing ridges having a height twicethe depth of the channel recess and formed by forging or cutting so asto be positioned alternately, when each of said pairs fitted togetherwith the recesses thereof opposed to each other, each of said pairs ofplates being fitted together to join top ends of the channel dividingridges on each plate of the pair to a flat surface of bottom wall of thechannel recess of the other plate opposed to said each plate and tothereby form U-shaped divided fluid passageways in the U-shaped fluidchannel inside the flat tube.
 6. A heat exchanger according to claim 1or 2 wherein each plate of said pairs has formed in a rear half of thechannel recess thereof channel dividing ridges having a height twice thedepth of the channel recess and formed by forging or cutting, thechannel recess of each plate having a front half in the form of a flatsurface provided by a bottom wall thereof and having no channel dividingridges, each of said pairs of plates being fitted together with therecesses thereof opposed to each other to join top ends of the channeldividing ridges thereof to the bottom wall flat surface of the channelrecess of the plate opposed to the dividing ridges and to thereby formU-shaped divided fluid passageways in the U-shaped fluid channel insidethe flat tube.
 7. A heat exchanger comprising ridged plates each havinga peripheral ridge provided on one side of the plate along a peripherythereof and a central ridge provided on said one side of the plate at acenter of the width thereof and extending downward from an upper end ofthe plate to a position where a return channel can be formed, the ridgesbeing formed by forging or cutting, each of the ridged plates having aU-shaped channel recess formed inwardly of the peripheral ridge andcomprising a front and a rear channel recess portion formed on oppositesides of the central ridge and a return channel recess portionpositioned under the central ridge, the channel recess having one of twofluid inlet-outlet through holes formed at one end thereof and the otherthrough hole formed at the other end thereof, each of the ridged plateshaving a flat surface on the other side thereof and being fitted to eachof flat plates face-to-face, each of said flat plates having the samecontour and the same size as the ridged plate and two fluid inlet-outletthrough holes corresponding to said through holes, the peripheral ridgeof the ridged plate having a top end thereof joined to a peripheral edgeof the flat plate, the central ridge of the ridged plate having a topend thereof joined to a flat surface of a corresponding central portionof the flat plate, whereby a flat tube having a U-shaped fluid channelinside thereof is formed so that a plurality of flat tubes are arrangedin parallel with a header member interposed between upper ends of eachpair of adjacent flat tubes to provide a front and a rear header incommunication with the upper ends of the said pair of adjacent flattubes, the header member comprising a pair of front and rear fluidpassing tube portions in communications with the respective inlet-outletthrough holes of the plates of said pair of adjacent flat tubes and aconnecting portion between the tube portions.
 8. A heat exchangercomprising ridged plates each having an edge ridge U-shaped in itsentirety and provided on one side of the plate along opposite side edgesand a lower edge thereof and a central ridge provided on said one sideof the plate at a center of the width thereof and having a bifurcatedupper end, the central ridge extending from the upper end downward to aposition where a return channel can be formed, the ridges being formedby forging or cutting, each of the ridged plates having a U-shapedchannel recess formed inwardly of the U-shaped edge ridge and comprisinga front and a rear channel recess portion formed on opposite sides ofthe central ridge and a return channel recess portion positioned underthe central ridge, each of the ridged plates having a flat surface onthe other side thereof and being fitted to each of flat platesface-to-face, each of said flat plates having the same contour and thesame size as the ridged plate, the peripheral ridge of the ridged platehaving a top end thereof joined to a peripheral edge of the flat plate,the central ridge of the ridged plate including the bifurcated upperends having a top end thereof joined to a flat surface of acorresponding central portion of the flat plate, whereby a flat tubehaving bifurcated open upper ends and a U-shaped fluid channel insidethereof is formed, a pair of front and rear header members being each inthe form of a pipe having a rectangular cross section, each of theheader members having slits formed in a lower wall thereof and arrangedat a predetermined spacing, a plurality of flat tubes being arranged inparallel by inserting the bifurcated open upper ends thereof into therespective slits in the front and rear header members to join the flattubes to the header members and to provide a front and a rear header incommunication with the bifurcated open upper ends of the flat tubes. 9.A heat exchanger according to claim 7 or 8 wherein a plurality ofchannel dividing U-shaped ridges are formed in the U-shaped channelrecess of each ridged plate by forging or cutting, and each ridged plateand each flat plate are fitted together face-to-face with the channeldividing U-shaped ridges of the ridged plate joined to the flat surfaceof the corresponding central portion of the flat plate to form aplurality of U-shaped divided fluid passageways in the U-shaped fluidchannel inside the flat tube.
 10. A heat exchanger comprising pairs ofplates with each plate of the pairs having a peripheral ridge providedon one side of the plate along a periphery thereof and a central ridgeprovided on said one side of the plate at a center of the width thereofand extending vertically, the ridges being formed by forging or cutting,each plate of said pairs having a front and a rear channel recessportion formed inwardly of the peripheral ridge on opposite sides of thecentral ridge, each of the front and rear channel recess portions havinga through hole formed in each of upper and lower ends thereof, eachplate of said pairs having a flat surface on the other side thereof,each of said pairs of plates being fitted together with their channelrecess portions opposed to each other to join the opposed peripheralridges to each other end-to-end and the opposed central ridges to eachother end-to-end and to thereby form a flat tube having a front and arear fluid channel inside thereof so that a plurality of flat tubes arearranged in parallel with an upper and a lower header member interposedrespectively between upper ends of each pair of adjacent flat tubes andbetween lower ends thereof to provide an upper and a lower header incommunication with the upper ends and the lower ends of said pair ofadjacent flat tubes, each of the header members comprising a pair offront and rear fluid passing tube portions in communications with thecorresponding through holes of the plates of said pair of adjacent flattubes and a connecting portion between the tube portions.
 11. A heatexchanger comprising pairs of plates with each plate of the pairs havinga side edge ridge provided on one side of the plate along each ofopposite side edges thereof and a central ridge provided on said oneside of the plate at a center of the width thereof and having abifurcated upper and a bifurcated lower end, the ridges being formed byforging or cutting, each plate of said pairs having a front and a rearchannel recess portion formed inwardly of the side edge ridges onopposite sides of the central ridge, each plate of said pairs having aflat surface on the other side thereof, each of said pairs of platesbeing fitted together with their channel recess portions opposed to eachother to join the opposed side edge ridges to each other end-to-end andthe opposed central ridges including the bifurcated upper and lower endsto each other end-to-end and to thereby form a flat tube havingbifurcated open upper and lower ends and a front and a rear fluidchannel inside thereof, an upper pair of front and rear header membersand a lower pair of front and rear header members being each in the formof a pipe having a rectangular cross section, each of the header membershaving slits formed in an upper wall or a lower wall thereof andarranged at a predetermined spacing, a plurality of flat tubes beingarranged in parallel by inserting the bifurcated upper or lower endsthereof into the respective slits in the header members to join the flattubes to the header members and to provide an upper pair of front andrear headers and a lower pair of front and rear headers in communicationwith the bifurcated upper and lower ends of the flat tubes respectively.12. A heat exchanger according to claim 10 or 11 wherein a plurality ofchannel dividing ridges are formed in the front and rear channel recessportions of each plate by forging or cutting, and each of said pairs ofplates are fitted together with their recess portions opposed to eachother to join each of opposed pairs of the channel dividing ridges toeach other end-to-end and form divided fluid passageways in the frontand rear fluid channels inside thereof.
 13. A heat exchanger accordingto claim 10 or 11 wherein each plate has formed in the respective frontand rear channel recess portions thereof front and rear channel dividingridges having a height twice the depth of the recess portion, the frontand rear channel dividing ridges being formed by forging or cutting andpositioned alternately when each of said pairs of plates are fittedtogether with their recess portions opposed to each other, each of saidpairs of plates being fitted together face-to-face to join top ends ofthe front and rear channel dividing ridges to a bottom wall flat surfaceof recess portion of the plate opposed thereto and to thereby formdivided fluid passageways in the front and rear fluid channels insidethe flat tube.
 14. A heat exchanger according to claim 10 or 11 whereineach plate of the pairs has formed in each of the front and rear channelrecess portions thereof a channel dividing ridge having a height twicethe depth of the recess portion, the channel dividing ridge being soformed by forging or cutting that the front and rear channel dividingridges of each pair of plates as fitted together face-to-face arepositioned alternately, each pair of plates being fitted together withtheir recess portions opposed to each other to join top ends of thefront and rear channel dividing ridges of each plate of the pair to abottom wall flat surface of the recess portion of the other plate of thepair opposed thereto and to thereby form divided fluid passageways inthe front and rear fluid channels inside the flat tube.
 15. A heatexchanger according to claim 10 or 11 wherein each plate has formed inone of the front and rear channel recess portions thereof a plurality ofchannel dividing ridges having a height twice the depth of the recessportion, the channel dividing ridges being formed by forging or cutting,the other channel recess portion having a bottom wall flat surfacehaving no channel dividing ridges, each of said pairs of plates beingfitted together with their recess portions opposed to each other to jointop ends of the channel dividing ridges to the bottom wall flat surfaceof the recess portion of the plate opposed thereto and to thereby formdivided fluid passageways in the front and rear fluid channels insidethe flat tube.
 16. A heat exchanger comprising ridged plates each havinga peripheral ridge provided on one side of the plate along a peripherythereof and a central ridge provided on said one side of the plate at acenter of the width thereof and extending vertically, the ridges beingformed by forging or cutting, each the ridged plates having a front anda rear channel recess portion formed inwardly of the peripheral ridge onopposite sides of the central ridge, each of the front and rear channelrecess portions having a through hole formed in each of upper and lowerends thereof, each of the ridged plates having a flat surface on theother side thereof and being fitted to each of flat plates face-to-face,each of said flat plates having the same contour and the same size asthe ridged plate and fluid inlet-outlet through holes corresponding tosaid through holes, the peripheral ridge of the ridged plate having atop end thereof joined to a peripheral edge of the flat plate, thecentral ridge of the ridged plate having a top end thereof joined to aflat surface of a corresponding central portion of the flat plate,whereby a flat tube having a front and a rear fluid channel insidethereof is formed so that a plurality of flat tubes are arranged inparallel with an upper and a lower header member interposed respectivelybetween upper ends of each pair of adjacent flat tubes and between lowerends thereof to provide an upper and a lower header in communicationwith the upper ends and the lower ends of said pair of adjacent flattubes, each of the header members comprising a pair of front and rearfluid passing tube portions in communications with the correspondingthrough holes of the plates of said pair of adjacent flat tubes and aconnecting portion between the tube portions.
 17. A heat exchangeraccording to claim 16 wherein the connecting portion of one of the upperand lower header members interposed between the upper ends and lowerends of each pair of adjacent flat tubes has a passage interconnectingthe fluid passing tube portions of the header member.
 18. A heatexchanger comprising ridged plates each having a side edge ridgeprovided on one side of the plate along each of opposite side edgesthereof and a central ridge provided on said one side of the plate at acenter of the width thereof and having a bifurcated upper and abifurcated lower end, the ridges being formed by forging or cutting,each of the ridged plates having a front and a rear channel recessportion formed inwardly of the side edge ridges on opposite sides of thecentral ridge, each of the ridged plates having a flat surface on theother side thereof and being fitted to each of flat plates face-to-face,each of said flat plates having the same contour and the same size asthe ridged plate, the side edge ridges of the ridged plate having topends thereof joined to side edges of the flat plate, the central ridgeof the ridged plate including the bifurcated upper and lower ends havinga top end thereof joined to a flat surface of a corresponding centralportion of the flat plate, whereby a flat tube having bifurcated openupper and lower ends and a front and a rear fluid channel inside thereofis formed, an upper pair of front and rear header members and a lowerpair of front and rear header members being each in the form of a pipehaving a rectangular cross section, each of the header members havingslits formed in an upper wall or a lower wall thereof and arranged at apredetermined spacing, a plurality of flat tubes being arranged inparallel by inserting the bifurcated upper or lower ends thereof intothe respective slits in the header members to join the flat tubes to theheader members and to provide an upper pair of front and rear headersand a lower pair of front and rear headers in communication with thebifurcated upper and lower ends of the flat tubes respectively.
 19. Aheat exchanger according to claim 16 or 18 wherein each of the ridgedplates has channel dividing ridges formed in the respective front andrear channel recess portions thereof by forging or cutting, and eachridged plate is fitted to each flat plate face-to-face to join top endsof the channel dividing ridges to a flat surface of a correspondingportion of the flat plate and to thereby form divided fluid passagewaysin the front and rear fluid channels inside the flat tube.
 20. A heatexchanger according to any one of claims 1, 7, 10 and 16 wherein theheader member interposed between the ends of each pair of adjacent flattubes has its fluid passing tube portions joined at their opposite endfaces to the flat surfaces on the other sides of the opposed plates ofthe pair of flat tubes.
 21. A heat exchanger according to in any one ofclaims 1, 7, 10 and 16 wherein tacks for temporarily holding the headermember are provided respective edges defining the inlet-outlet throughholes in the end of each plate.
 22. A heat exchanger according to anyone of claims 3 to 6, 9, 12 to 15 and 19 wherein a plurality of cutoutsare formed in the channel dividing ridges on each plate to cause theadjacent divided fluid passageways inside the flat tube to communicatewith each other through the cutouts.
 23. A heat exchanger according toany one of claims 1, 2, 7, 8, 10, 11,16 and 18 wherein a fin is providedbetween each pair of adjacent flat tubes included in the flat tubesarranged in parallel, and the fin has opposite sides edges thereofjoined to the flat surfaces on the other sides of the plates of the pairof flat tubes.